Shijia Ling; He Ren; Rui Zhang; Yue Liu; Boping Liu; Ruihua Cheng
Abstract
The chromium/vanadium bimetallic Phillips catalysts developed by our research group have been proved to be a promising process to produce bimodal polyethylene using a single-reactor process. The vanadium loading of CrV-1/1, CrV-1/2, and CrV-1/3 has a significant effect on the polymerization activity, ...
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The chromium/vanadium bimetallic Phillips catalysts developed by our research group have been proved to be a promising process to produce bimodal polyethylene using a single-reactor process. The vanadium loading of CrV-1/1, CrV-1/2, and CrV-1/3 has a significant effect on the polymerization activity, product molecular weight (MW), as well as the molecular weight distribution (MWD). Due to the unstable and easy deactivation of vanadium active centers at atmospheric or low (0.4 MPa) reaction pressure [Macromol. React. Eng. 2015, 9, 462–472], the reaction is carried out at 1.0 MPa to strength the V active center on the activities of ethylene homopolymerization, ethylene/1-hexene copolymerization, and the H2 responds properties. The reaction carried out at higher pressure promotes the polymerization activities. With the same amount of cocatalyst, the highest activity of the three Cr-V bimetallic catalysts CrV-1/1, CrV-1/2 and CrV-1/3 decreases with the increase of vanadium loading. The Cr-V bimetallic catalysts require more cocatalyst than the single metal Cr cat. It was found two obvious peaks in the GPC curves of homopolyethylen and ethylene/1-hexene copolymer. It means that the higher reaction pressure benefits the promotion of the active center of catalyst for higher MW. By increasing the loading from 0.48 wt.% (CrV-1/1) to 0.96 wt.% (CrV-1/2), the molecular weight increases by nearly 30%. Besides, according to the deconvolutions of the GPC curves of homopolymers, ethylene/1-hexene copolymers, and the homopolymers with H2 modulation, the synergetic effect between Cr and V center is presented. As the vanadium loading increases, the active site accounted for the high molecular weight portion increases, and the Cr-V catalyst presents better hydrogen responds. When the partial pressure of hydrogen is 0.1 MPa, the molecular weight is reduced by nearly half. Specifically, the high molecular weight peak is weakened, while the low molecular weight peak is strengthened. The peak position does not change significantly. The higher vanadium content and the greater sensitivity of hydrogen modulation indicate that the vanadium active center has better hydrogen responds than the chromium active center does. The homopolymerization product of the Cr/V-1/1 catalysts exhibits higher tensile strength and elongation-at-break. The tensile properties of the copolymerized product of CrV-1/1 are further improved.
Olefin oligomerization
Tanja H. Ritter; Helmut G. Alt
Abstract
Nine different bis(arylimino)pyridine complexes of Fe(III) with different halide substituents (F, Cl, Br, I) at different positions of the iminophenyl group of the ligand have been synthesized, characterized and applied for homogeneous 1-pentene and 1-hexene oligomerization and co-oligomerization reactions ...
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Nine different bis(arylimino)pyridine complexes of Fe(III) with different halide substituents (F, Cl, Br, I) at different positions of the iminophenyl group of the ligand have been synthesized, characterized and applied for homogeneous 1-pentene and 1-hexene oligomerization and co-oligomerization reactions after activation with methylaluminoxane (MAO). The best activity in 1-hexene oligomerization (152 kg/mol.h) was observed for 4/ MAO with an iodine substituent in para position of the iminophenyl group. Fluorine substituents in the meta position of the iminophenyl group proved as disadvantageous (1 kg/mol.h) in homo-oligomerization reactions but advantageous in co-oligomerization reactions of 1-pentene and 1-hexene. Obviously, tiny electronic or steric differences at the active sites of the corresponding catalysts are responsible for this result (structure-property relationship). The product distributions of the co-dimerization reactions of 1-pentene and 1-hexene reflected a binominal behaviour with dominating co-products. The ratio of dimers is 1:2:1 (C10:C11:C12) while the trimers (pentadecenes up to octadecenes) show proportions of 1:3:3:1.
Composites and nanocomposites
Afshar Alihosseini; Amin Hedayati Moghaddam
Abstract
In this work, the effects of operative parameters on CH4, CO2, O2, and N2 membrane gas separation for poly (4-methyl-1-pentane) (PMP) membrane modified by adding nanoparticles of TiO2, ZnO, and Al2O3 are assessed and investigated. The operative parameters were type and percentage of nanoparticles, and ...
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In this work, the effects of operative parameters on CH4, CO2, O2, and N2 membrane gas separation for poly (4-methyl-1-pentane) (PMP) membrane modified by adding nanoparticles of TiO2, ZnO, and Al2O3 are assessed and investigated. The operative parameters were type and percentage of nanoparticles, and cross membrane pressure. The membrane permeability and selectivity were selected as the responses and indexes of separation process performance. To design the experimental layout, design of experiment methodology (DoE) techniques were used. Further, the separation process was modeled and simulated using artificial intelligence (AI) methods. So, a robust black-box model based on radial basis function (RBF) network was developed and trained with the ability for predicting the performance of membrane process. The developed model could simulate the process and predict the permeability with R2-validation of 0.9. Finally, it was found that addition of nanoparticles and increasing the operative pressure had positive effects on membrane performance. Maximum permeability values for O2, N2, CO2 and CH4 were 181.58, 52.09, 550.85, and 54.26, respectively. The maximum values of validation-R2 of optimum structure for CO2/N2 and CO2/CH4 selectivity were 0.8697 and 0.7028, respectively.
Polymer processing
Moammadreza Nakhaei; Ali Ahmadi; Ghasem Naderi
Abstract
Polyamide 6 / nitrile butadiene rubber / nanoclay (PA6/NBR/clay) nanocomposite has gathered wide acceptance in industry. Laser welding, as a fabrication method, is applied to welding of polymer nanocomposites. In this study, the input parameters (clay (Closite 30B) content, laser power, scan velocity ...
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Polyamide 6 / nitrile butadiene rubber / nanoclay (PA6/NBR/clay) nanocomposite has gathered wide acceptance in industry. Laser welding, as a fabrication method, is applied to welding of polymer nanocomposites. In this study, the input parameters (clay (Closite 30B) content, laser power, scan velocity and stand-off-distance) are varied to achieve the best responses (tensile strength of welds). Response surface methodology (RSM) is utilized to investigate the effect of input parameters on mechanical properties. Morphology and tensile properties of nanocomposites were observed with scan electron microscopy (SEM), transmission electron microscopy (TEM) and tensile test. The results demonstrated that increasing the clay content from 1 to 5%wt and stand-off-distance from 4 to 8 mm decreased tensile strength of welds about 15% and 5%, respectively. The tensile strength of PA6/NBR composite is 25.6, whereas the prediction models showed that under optimal conditions of laser power of 105 W, scan velocity of 300 mm/min and stand-off-distance of 4 mm, the maximum tensile strength of PA6/NBR nanocomposite with 1, 3 and 5 % nanoclay are 27.2 MPa, 27.6 MPa and 24.7 MPa, respectively. These tensile strengths are about 99, 89 and 73% of the strength of these nanocomposites before welding.
Polyolefin degradation
Sara Zarei; Gholam-Reza Nejabat; Mohammad-Mahdi Mortazavi; Soheyl KhajehPour-Tadavani
Abstract
Varying amounts of an amorphous poly(1-hexene) (PH, Mv 1.7×106 Da) were added to an LLDPE matrix containing 3% w/w Addiflex oxo-biodegradable additive (HES-W) and extruded and converted into films. Then the effect of presence of PH was investigated on microstructure, thermal and tensile behavior ...
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Varying amounts of an amorphous poly(1-hexene) (PH, Mv 1.7×106 Da) were added to an LLDPE matrix containing 3% w/w Addiflex oxo-biodegradable additive (HES-W) and extruded and converted into films. Then the effect of presence of PH was investigated on microstructure, thermal and tensile behavior of polymer films before and after 6 weeks of ultra violet irradiation (UVR). Due to UVR, viscosity average molecular weight (Mv) of the sample without PH decreased from 9.6×104 to 4.6×103 Da and for the sample containing 3% w/w PH from 11.3×104 to 3.0×104 Da, also carbonyl index (CI) of the sample without PH increased from 0 to 28.7 while for the sample containing 3% w/w PH increased from 1.8 to 30.4. Moreover, differential scanning calorimetry (DSC) showed that crystallinity of the sample without PH increased from 34.4% to 36.9% and from 28.7% to 32.1% for the sample containing 3% w/w PH. Thermal gravimetric analysis (TGA) showed lower decomposition temperature for the samples containing PH. The elongation-at-break decreased from 723.0% to 88% for the sample without PH and from 410% to 10% for the sample containing PH. Atomic force microscopy (AFM) indicated smoother surfaces for samples containing 3% w/w PH before and after UVR. Although, the aforementioned results showed that the presence of limited amounts of PH in the LLDPE matrix deteriorated thermal and mechanical properties of the matrix, it hindered the oxo-biodegradablity of the matrix by opposing assimilation process perhaps due to high Mv and/or gelation.
Seyed Mehdi Ghafelebashi Zaranda; Ali Safinejad
Abstract
In this study, slurry polymerization kinetics of ethylene with TiCl4/Mg(OEt)2/AlR3 Ziegler-Natta catalysts in various conditions using the model of sum square error (SSE) (method I) and model of least square error (LSE) (Method II) was investigated. For this purpose the molecular weight distributions ...
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In this study, slurry polymerization kinetics of ethylene with TiCl4/Mg(OEt)2/AlR3 Ziegler-Natta catalysts in various conditions using the model of sum square error (SSE) (method I) and model of least square error (LSE) (Method II) was investigated. For this purpose the molecular weight distributions of the samples were deconvoluted to the minimum number of Flory type distributions where each represents a different active center type of Ziegler-Natta catalyst. The first method used to determine the leading apparent polymerization kinetic constants for each site in absence of hydrogen by simultaneously fitting the instantaneous polymerization rate, cumulative polymer yield, and molecular weight distribution measured for various samples with various conditions. Second method was used to determine all kinetics parameters such as initiation, propagation, termination and transfer to monomer reaction in absence and also in the presence of hydrogen. For the later, transfer to hydrogen also determined. The results showed that this simulation package is a powerful tool for design and scale up this kind of processes.
